Cooling means for thermionic valves



March 8, 1938. E, PRIVETT 2,110,774

COOLING MEANS FOR THERMIONIC VALVES Filed Jan. 16, 1935 INVENTOR, PERCY EDWARD PRIVETT Patented Mar. 8, 1938 UNITED STATES PATENT OFFICE COOLING MEANS FOR THERMIONIC VALVES Application January 16, 1935, Serial No. 2,061 In Great Britain February 3, 1934 5 Claims.

This invention relates to methods of and means for cooling thermionic valves and more specifically to thermionic valve cooling arrangements of the kind in which an electrode or electrodes of a thermionic valve or valves is or are cooled by means of a cooling fluid in heat contact therewith.

A well known form of thermionic valve in common use in wireless and similar transmitters is that in which the anode of the valve forms part of the envelope thereof, and it is common at the present time to cool such valves by providing a jacket about the anode and causing water to flow into and through said jacket, A difficulty of water cooled systems of this kind is that the amount of water provided, and therefore the general size of the apparatus, is somewhat large;

an elevated tank or other pressure system e. g.'

a pump of relatively large capacity, is necessary to provide the required water flow, and there is the danger of damage in the event of stoppage or failure of a pump (if employed).

According to this invention, an electrode or electrodes of a thermionic valve or valves is or are cooled by means of a jacket or jackets adapted to contain liquid and forming part of a cooling system of such dimensions and design that the heat generated by the electrode or electrodes to be cooled is sufficient to boil off said liquid from the said jacket. or jackets so that almost the whole or at any rate the major part of the cooling is effected by reason of the latent heat of evaporation of said liquid. This invention will best be understood by referring to the accompanying drawing in which:

Figure 1 is a simple schematic diagram of the invention;

Figure 2 is an elevation, partly in section, of a water jacket;

Figure 3 is a modification of the schematic diagram of Figure 2;

Figure 4 is a schematic diagram of the multivalve arrangement having one or more pumps in a common conductor.

In one embodiment of the invention the jacket or jackets is or are included in a closed or loop system incorporating a condenser said system containing insuflicient water to fill it and said condenser being so positioned as to operate as a radiator-condenser to condense to water, steam which has been'boiled off from the jacket or jackets, said water being returned to said jacket or jackets.

An arrangement of this kind will now be described with reference to Figure 1 which is illustrative in a purely schematic manner of the principle of the invention.

In Figure 1 a thermionic valve a of the kind in which the anode forms part of the envelope, is insert-ed anode downwards into a jacket or first 5 chamber B, the valve being so positioned and arranged that the usual seal between the customary metal anode and glass portion of the envelope is outside the jacket.

From a point at or near the upper end of the 10 jacket an upwardly sloping steam pipe C leads into a second chamber E which constitutes a condenser. The steam pipe C leads into said chamber E near its lowest point the said chamber having transverse tubes running across it .15 and communicating at both ends with the outside air or the chamber may consist in whole or in partof a so-called honeycomb radiator. A motor driven fan J or other means for drawing cooling air through the tubes or honeycomb openings so as to condense the steam in the radiator is provided. a

The lower portion of the condenser is connected by the pipe F to a third chamber G the upper portion of which is situated at a level slightly above that of the upper portion of the jacket B. This chamber G is in turn connected to one end of a pipe D the other end of which sweeps upwards towards and is connected to the lower end of the jacket B. 3o

A relief valve in the form of a syphon tube M is shown fitted to the top of the chamber G but may be fitted to any other part of the system as determined by the lay-out.

Sufficient water is poured into the arrangement, for example, through a filler (not shown) above the condenser to fill the apparatus up to a level about the bottom and of the steam pipe C. Before the apparatus is started the condenser E will be full of air but this air will be displaced 40 through the relief valve or equivalent device M and be replaced wholly or in part by steam when operation is proceeding. The syphon tube M seals itself with condensed vapour shortly after the air is expelled.

If desired, the condenser E may have a permanent opening at the top but the condenser should then be of suiiicient capacity to prevent the escape of any uncondensed vapour.

In operation when the valve anode becomes hot, water in the jacket is boiled off and passes up the steam pipe into the condenser to be condensed by the cooling surfaces thereof, the condensate falling through the pipe F into the chamber G and flowing therefrom to the bottom oi the jacket to replace water which has been evaporated.

If desired the whole apparatus may be made pressure tight and may be designed to operate at an appreciable pressure above atmosphere in which case a relief valve is fitted to the condenser and loaded to the required extent to prevent rise 01 pressure above a predetermined value.

It will be appreciated that with apparatus in accordance with this invention substantially the whole or at any rate the major portion of the cooling will be eflected by reason of the latent heat or steam and because of the high value of this latent heat the amount of water required and therefore the size of the whole apparatus will be relatively small.

As at a given pressure the boiling point of a fluid is fixed it is not possible for any part of the apparatus to reach more than a predetermined temperature, and a fixed quantity of water (approximately .06 lb. per minute) is evaporated, for each kw. being dissipated at the valve anode.

Precautions should be taken e. g. by suitable arrangement of piping to ensure that the fiow of steam from the jacket is through the upper pipe C and not blown out through the return pipe D.

A special form of water jacket which assists in inducing the correct circulation in the system is illustrated in the accompanying Figure 2 which is a half sectional elevation of the jacket in question. The central cylindrical water jacket proper B is provided with a plurality of circulation tubes A symmetrically arranged around the outside of the cylindrical jacket which tend to cause an upward flow of water in the jacket proper by reason of the difference in density between the mixture of steam and water in the jacket proper and the water in the tubes A. This difference in density is due mainly to the fact that the steam in the steamwater mixture in the in the annular space Al- The steam leaves the space A1 through pipes A: and flows into a circular pipe or header As. C and D correspond to the steam and water pipes shown in Figure 1. The anode portion oi! valve a is shown in dotted lines as being centrally located within jacket B.

A modified system which is preferred in practice is illustrated schematically in the accompanying Figure 3. In this arrangement an auxiliary chamber A is employed which serves to collect steam boiled oil in the jacket B and led to the chamber A by means of a pipe A". The chamber A is connected to the condenser E by means oi the steam pipe C and also as shown by means of a pipe A"" to the chamber G. A pipe F connects the condenser E with the chamber G and a small pump P, preferably of the gear type, is located in the pipe D joining the chamber G and the bottom of the jacket, said pump maintaining a constant circulation in the required direction. The disposition of the piping is such that steam rises in the pipe C and water descends in the pipe A'.

A further modification involves the use of a relief valve in the pipe A" set to open at a pressure which may be appreciably above atmospheric pressure. This relief valve maintains a pressure in the jacket and associated piping but allows water at above 212 F. to flow into the chamber A which is at atmospheric pressure or less. A portion of this water is immediately formed into steam which is in turn condensed in the condenser.

.This arrangement shown in Fig. 3 involves the jacket proper is collected use of a pump or pumps to .take the condensate from the condenser back into the water system of which the jacket or jackets form part.

With this arrangement there will be water circulation between the jacket and the chamber G and the main. purpose of this water circulation size of the whole apparatus may be made quite small (b) that there is no danger of damage in the event of failure of a pump, for no pump need be provided, and even it there be a pump in the water cooling circulating system (if any) it is not an important factor as regards cooling (c) that there is no danger of damage due to the condenser freezing because the said condenser does not contain water, (d) that there should be no loss 0! water or steam as the whole apparatus may be arranged to be operated. at or substantially at atmospheric pressure although, if desired, a ball cock and independent water supply may be fitted to maintain the correct water level in the apparatus (e) that no preparation is necessary for starting up or shutting down, (I) that there is considerable economy as compared to a water cooling system by reason oi the relatively high cost of the water in such a system. Such water must, of course, be pure so as to be of the necessary electrical high resistance and so as not to give rise to electrolytic and chemical action on the metal with which it comes in contact. The cost 01 the water in a water cooling system arises both as a matter of first cost and as a matter of providing replacement water to make up for losses, e. g. by evaporation. As regards the latter point, it will be realized that the effect of evaporation in a water cooling system is to increase the percentage impurity in the remaining water, which impurity tends to deposit on the hottest parts of the apparatus and greatly reduces the cooling efficiency. In fact the question of obtaining and maintaining a high degree of purity in the water 01' a water-cooled valve transmitter is a highly important matter practically, and has given great difliculty in the past, so that the present invention, by greatly reducing the bulk of water necessary, is of great practical advantage from this aspect of purity. Indeed this advantage is greater than would at first sight appear, because, in the steam systems of the present invention, the agitation of the water by boiling tends to throw down any dissolved impurities in the form of a. relatively innocuous sludge instead of in the form of a hard deposit upon the most highly heated parts oi! the apparatus: (g) that the possibility of effecting cooling at atmospheric pressure (in contradistinction to water cooling systems which generally involve that the pressure of the water in the water jackets will be well above atmospheric pressure) involves an obvious diminution in the cost of, and care needed in making, pipe and similar joints and an obvious diminution of liability to damage to nearby apparatus by reason of water or vapour escaping under pressure; and (k) that the high resistance of a column of steam as compared to a column of water is an important electrical advantage.

If desired, steam cooling at less than 212 F. may be effected by providing a condenser pump as well known per se in steam engineering practice.

Again, if desired the heat generated in the system may be utilized for heating and other purposes, e. g. the condenser system could be constructed and arranged to operate as a heater for the air within a station" containing the apparatus and the arrangement could easily be made such as not to cause excessive draughts.

Although pumps are not necessary in carrying out this invention, in the case of a multi-valve installation it may be of advantage to employ one or more pumps and a common condenser for a plurality of jackets provided one for each valve. An arrangement of this kind which is generally similar to that shown in Figure 3 is shown schematically in the accompanying Figure 4. In this arrangement an auxiliary chamber A is employed which serves to collect steam boiled off i in the several jackets B and led to the common chamber A by means of the pipes A". The chamber A is connected to the condenser E by means of the steam pipe C and also as shown by means of a pipe A to the chamber G. A pipe F connects the condenser E with the chamber G and a small pump P, preferably of the gear type, is located in the pipes D joining the chamber G and the bottom of each jacket and maintains a constant circulation in the required direction. One pump may serve one'or a plurality of jackets. The disposition of the piping is such that steam rises in the pipe C and water descends in the pipe A'. The reference numerals in Figure 4 correspond to those in Figure 3 and it is believed that further description is unnecessary. The pumps in this case need be only quite small and are preferably of the gear type.

For electrical reasons governed by the circuit in which the valve or valves are used it may be necessary to insulate from earth the whole plant in which case the motor or motors driving the pump or pumps (if used) may be fitted with an insulating coupling or the pump or pumps may be driven by a belt of insulating material or the motor may be wound to run off alternating current and be provided with a double-wound isolating transformer. Alternatively, insulating pipe coils maybe fitted at convenient points in the pipe system so as to allow certain parts to remain at a high potential above earth.

Having now particularly described and ascertained the nature of my said invention and in what manner. the same is to be performed, I declare that what I claim is:-

1. A system for cooling a thermionic valve, a cooling jacket associated with the anode of said valve, said jacket having a plurality of externally located circulating tubes, a condenser, a chamber adapted to receive condensate from said condenser, an auxiliary chamber, a pipe connecting said jacket to said auxiliary chamber the top of which is located above the top of said jacket, a pipe connecting said auxiliary chamber to said first mentioned chamber, a pipe leading from a point near the top of said auxiliary chamber to the condenser, a pipe connecting the condenser with said first mentioned chamber, a return connection between said first mentioned chamber and said jacket, a pump for inducing circulation in the loop path inter-connecting said auxiliary chamber, said first mentioned chamber and said jacket.

2. A system for cooling a thermionic valve, a cooling jacket associated with the anode of said valve, a condenser wherein the cooling liquid circulates within a closed path, a lightly loaded relief valve on said condenser, a chamber adapted to receive condensate from said condenser, an

auxiliary chamber, a pipe connecting said jacket to said auxiliary chamber the top of which is located above the top of said jacket, a pipe connecting said auxiliary chamber to said first mentioned chamber, a pipe leading from a point near the top of said auxiliary chamber to the condenser, a pipe connecting the condenser with the said first mentioned chamber, a return connection between said first mentioned chamber and said jacket, a pump for inducing circulation in the loop path inter-connecting said auxiliary chamber, said first mentioned chamber and said jacket.

3. A system for cooling a thermionic valve, a cooling jacket associated with the anode of said valve, a condenser, a chamber adapted to receive condensate from said condenser, an auxiliary chamber, a pipe connecting said jacket to said auxiliary chamber the top of which is located above the top of said jacket, a pipe leading from a point near the top of said auxiliary chamber to the condenser, a pipe connecting the condenser with the said first mentioned chamber, a return connection between said first mentioned chamber and said jacket, a pump for inducing circulation in the loop path inter-connecting said auxiliary chamber, said first mentioned chamber and said jacket.

4. A system as claimed in claim 3 comprising a relief valve located at an intermediate point between the jacket and the return connection of said jacket substantially as and for the purpose described.

5. A system for cooling a thermionic valve, a cooling jacket associated with the anode of said valve, a'condenser, a chamber adapted to receive condensate from said condenser, means for supplying cooling air to said condenser, an auxiliary chamber, a pipe connecting said jacket to said auxiliary chamber the top of. which is located above the top of said jacket, a pipe leading from a point-near the top of said auxiliary chamber to the condenser, a pipe connecting the condenser with the said first mentionedchamber, a return connection between said first mentioned chamber and said Jacket, a pump for inducing circulation in the loop path inter-connecting said auxiliary chamber, said first mentioned chamber and said jacket.

PERCY EDWARD PRIVEIT. 

